1. Field of the Invention
The invention relates to a apparatus having a housing which bounds an inner housing space, and which has a housing wall provided with sound transmission openings and which can be applied to an ear in the area of the sound transmission openings in an on-ear mode of the apparatus, during which, a wall portion of the housing wall, in which the sound transmission openings are situated, can be covered with the ear, and having an electroacoustic transducer accommodated in the inner housing space and arranged adjacent to the sound transmission openings, the transducer having a front volume and a rear volume, and being capable of generating sound which can be emitted into the acoustic free space via the front volume and through the sound transmission openings, the rear volume being open to the inner housing space, and having at least one passage which traverses a housing wall and which, together with the inner housing space and the rear volume of the transducer, the rear volume being open to the inner housing space, forms an absorption-circuit resonator which causes a dip in the sound pressure versus frequency response when the apparatus operates in the on-ear mode, and having compensation means for compensating dip in the sound pressure versus frequency response.
2. Description of the Related Art
Such an apparatus of the type defined in the opening paragraph, is commercially available in various versions and is thus known. Such an apparatus is, for example, commercially available in the form of mobile telephones having the type designations S6 and S10. In the known apparatus, the compensation means for compensating dip in the sound pressure versus frequency response is formed by a digitally-operating electronic compensation circuit which is comparatively intricate and is, therefore, comparatively expensive, this apparatus further having the problem that the frequency range in which the dip in the sound pressure versus frequency response occurs may vary, the compensation provided by the electronic compensation circuit being at least significantly reduced or even lost.
It is an object of the invention to preclude the afore-mentioned problems and to provide an improved apparatus of the type defined in the opening paragraph, in which the desired result is achieved by simple compensation means.
According to the invention, in order to achieve this object in an apparatus of the type defined in the opening paragraph, the housing has been provided with at least one duct to form the compensation means, this at least one duct traversing the housing and being arranged outside the wall portion that can be covered with an ear, and adjacent to the rear volume of the transducer, and forming an acoustic friction.
By taking the measures in accordance with the invention, it is advantageously achieved, in a very simple manner, that the spurious absorption-circuit resonator is damped in such a manner that the undesired influence of the absorption-circuit resonator on the sound pressure versus frequency response in an on-ear mode of the apparatus is eliminated, or at least reduced to such an insignificant extent that no dip occurs in the sound pressure versus frequency response. A further advantage is that a correct and satisfactory reproduction of low-frequency signals is guaranteed with a comparatively small volume of the inner space of the apparatus, because the acoustic free space outside the apparatus, via the at least one duct, contributes to the reproduction of low-frequency signals, which facilitates the realization of an apparatus in accordance with the invention having minimal external dimensions. In practice, an apparatus in accordance with the invention has a plurality of such ducts, each forming an acoustic friction.
In an apparatus in accordance with the invention, each duct provided as an acoustic friction can be formed by a bore which traverses a housing wall and which, in the case of a plastic housing, can be formed during injection-molding of the housing. However, it has proven to be particularly advantageous if the housing comprises at least two housing sections which can be joined together, which adjoin each other in the area of a separating zone and have two wall portions in the area of the separating zone which adjoin one another in an acoustically impervious manner, and to form the at least one duct in the area of at least one wall portion, at least one trough-shaped recess which is open to this wall portion has been provided, this at least one recess being closed at its open side by the other wall portion. In this way, each duct forming an acoustic friction can be manufactured in a very simple manner and with a high precision, particularly if the housing is made of a plastic, in which case each recess can be formed during injection-molding of the relevant housing section.
In an apparatus in accordance with the invention it has further proven to be advantageous if the the housing has the shape of a rectangular parallelepiped and has a front main wall, a rear main wall, and four side walls, and the sound transmission openings have been provided in the front main wall, and the at least one duct has been provided in the area of a side wall adjacent to the transducer. Such a construction has proved to be very advantageous in practice.
The afore-mentioned as well as further aspects of the invention will become apparent from the embodiments described hereinafter and given by way of example and will be elucidated with reference to these embodiments.